Metal coordination in photoluminescent sensing

A FRET-based fluorescent Zn2+ sensor: 3D ratiometric imaging, flow cytometric tracking and cisplatin-induced Zn2+ fluctuation monitoring

Monitoring labile Zn²⁺ homeostasis is of great importance for the study of physiological functions of Zn²⁺ in biological systems. Here we report a novel ratiometric fluorescent Zn²⁺ sensor, CPBT, which was constructed based on chelation-induced alteration of FRET efficiency. CPBT was readily cell membrane permeable and showed a slight preferential localization in the endoplasmic reticulum. With this sensor, 3D ratiometric Zn²⁺ imaging was first realized in the head of zebra fish larvae via Z-stack mode. CPBT could track labile Zn²⁺ in a large number of cells through ratiometric flow cytometric assay. More interestingly, both ratiometric fluorescence imaging and flow cytometric assay demonstrated that the labile Zn²⁺ level in MCF-7 cells (cisplatin-sensitive) decreased while that in SKOV3 cells (cisplatin-insensitive) increased after cisplatin treatment, indicating that Zn²⁺ may play an important role in cisplatin induced signaling pathways in these cancer cells.

A Zn²⁺ sensor exhibiting 3D ratiometric imaging and flow cytometric ability was constructed based on the FRET mechanism, and cisplatin-induced endogenous labile Zn²⁺ fluctuations were monitored in real time.

Luminescent molecules towards precise cellular event regulation

A unique lanthanide complex which responds to near-infrared (NIR) stimulation was developed for remote regulation of cellular events. This molecule can be localized specifically on the cell surface. Upon NIR stimulation, strong emission of the complex can successfully modulate the activities of light-gated membrane channels and regulate the ion flux in vivo.

Cyanide Sensing in Water Using a Copper Metallogel through "Turn-on" Fluorescence

The development of fluorescent probes for selective detection of cyanide has gained considerable attention over the past two decades due to benefits like high selectivity as well as sensitivity, fast response, visual output, accurate quantification, and a simplified sample preparation procedure. However, the propensity of supramolecular gels toward fluorescence sensing of cyanide in aqueous medium is not well explored until now. Herein, we report the design and synthesis of a novel copper based metallogel capable of sensing cyanide in water by fluorescence "turn on". Toward this, a terpyridine attached poly(aryl ether) dendrone derivative (G1) is synthesized which forms gel and exhibits Aggregation Induced Emission (AIE). The addition and diffusion of copper ions to the gel resulted in the formation of a nonluminescent copper metallogel (CuG). The copper metallogel could selectively sense cyanide in water by a fluorescence "turn-on" signal due to the regeneration of the AIE active gel. The mechanistic pathways of the sensing have been studied, and the detection limit for sensing was found to be as low as 1.09 μM. A thin film of CuG was prepared by casting the gel and used as a test strip for the visual detection of cyanide in water.

Anthryl-Appended Platinum(II) Schiff Base Complexes: Exceptionally Small Stokes Shift, Triplet Excited States Equilibrium, and Application in Triplet-Triplet-Annihilation Upconversion

Two anthryl platinum(II) N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-benzenediamine Schiff base complexes were synthesized, with the anthryl attached via its 9 position (Pt-9An) or 2 position (Pt-2An) to the platinum (Pt) Schiff base backbone. The complexes show unusually small Stokes shifts (0.23 eV), representing a very small energy loss for the photoexcitation/intersystem crossing process, which is beneficial for applications as triplet photosensitizers. Phosphorescence of the Pt(II) coordination framework (Φ_P = 11.0%) is quenched in the anthryl-containing complexes (Φ_P = 4.0%) and shows a biexponential decay (τ_P = 3.4 μs/87% and 18.2 μs/13%) compared to the single-exponential decay of the native Pt(II) Schiff base complex (τ_P = 3.7 μs). Femtosecond/nanosecond transient absorption spectroscopy suggests an equilibrium between triplet anthracene (³An) and triplet metal-to-ligand charge-transfer (³MLCT) states, with the dark ³An state slightly lower in energy (1.96 eV for Pt-9An and 1.90 eV for Pt-2An) than the emissive ³MLCT state (1.97 eV for Pt-9An and 1.91 eV for Pt-2An). Intramolecular triplet-triplet energy transfer (TTET) and reverse TTET take 4.8 ps/444 ps for Pt-9An and 55 ps/1.7 ns for Pt-2An, respectively. The triplet-state equilibrium extends the triplet-state lifetime of the complexes to 103 μs (Pt-2An) or 163 μs (Pt-9An), in comparison to the native Pt(II) complex, which shows a lifetime of 4.0 μs. The complexes were used for triplet-triplet-annihilation upconversion with perylene as the triplet acceptor. The upconversion quantum yield is up to 15%, and a large anti-Stokes shift (0.75 eV) is achieved by excitation into the singlet metal-to-ligand charge-transfer absorption band (589 nm) of the complexes (anti-Stokes shift is 0.92 eV with 9,10-diphenylanthracene as the acceptor).

A pH-Responsive System Based on Fluorescence Enhanced Gold Nanoparticles for Renal Targeting Drug Delivery and Fibrosis Therapy

Background

Stimuli-responsive gold nano-assemblies have attracted attention as drug delivery systems in the biomedical field. However, there are challenges achieving targeted delivery and controllable drug release for specific diseases.

Materials and Methods

In this study, a glutathione (GSH)-modified fluorescent gold nanoparticle termed AuLA-GSH was prepared and a Co²⁺-induced self-assembly drug delivery platform termed AuLA-GSH-Co was constructed. Both the pH-responsive character and drug loading behavior of AuLA-GSH-Co were studied in vitro. Kidney-targeting capability was investigated in vitro and in vivo. Finally, the anti-fibrosis efficiency of AuLA-GSH-Co in a mouse model of unilateral ureteral obstruction (UUO) was explored.

Results

AuLA-GSH-Co was sensitive to pH changes and released Co²⁺ in acidic conditions, allowing it to have controllable drug release abilities. AuLA-GSH-Co was found to improve cellular uptake of Co²⁺ ions compared to CoCl₂ in vitro. AuLA-GSH exhibited specific renal targeting and prolonged renal retention time with low non-specific accumulation in vivo. Moreover, the anti-fibrosis efficiency of AuLA-GSH-Co was higher compared to CoCl₂ in a mouse model of unilateral ureteral obstruction (UUO).

Conclusion

AuLA-GSH-Co could greatly enhance drug delivery efficiency with renal targeting capability and obviously relieve renal fibrosis, providing a promising strategy for renal fibrosis therapy.

Turning on solid-state phosphorescence of platinum acetylides with aromatic stacking

Neat solids that phosphoresce under ambient conditions are rare due to aggregation-caused quenching. This communication describes a platinum acetylide (PtPE) that phosphoresces as a solid due to programmed aromatic stacking interactions of pendant groups that prevent intermolecular aggregation.

A novel luminescent Ir(iii) complex for dual mode imaging: synergistic response to hypoxia and acidity of the tumor microenvironment

The early detection of cancer shows great promise for the control and prevention of cancer. For early detection, one of the challenges that still exists is searching for methods that can illuminate tumors with high sensitivity. Here, acidity and hypoxia, two typical features that exist universally in a solid tumor microenvironment, were focused on to attain synergistic imaging with an enhanced signal-to-noise ratio. This was realized using an iridium(iii) based optical probe (Ir-1) that could sense acidity and hypoxia simultaneously and synergistically. Through the synergistic sensing of acidic pH and hypoxia, stronger emission signals or larger lifetime changes can be obtained than if a single factor (acidity or hypoxia) is used to induce variations. Furthermore, its potential for biological applications was confirmed by employing Ir-1 for phosphorescence synergistic intensity and lifetime imaging of acidity and hypoxia in live monolayer cells and 3D multicellular spheroids.

Small-molecule fluorescent probes for imaging gaseous signaling molecules: current progress and future implications

Endogenous gaseous signaling molecules including nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H2S) have been demonstrated to perform significant physiological and pharmacological functions and are associated with various diseases in biological systems. In order to obtain a deeper insight into their roles and mechanisms of action, it is desirable to develop novel techniques for effectively detecting gaseous signaling molecules. Small-molecule fluorescent probes have been proven to be a powerful approach for the detection and imaging of biological messengers by virtue of their non-invasiveness, high selectivity, and real-time in situ detection capability. Based on the intrinsic properties of gaseous signaling molecules, numerous fluorescent probes have been constructed to satisfy various demands. In this perspective, we summarize the recent advances in the field of fluorescent probes for the detection of NO, CO and H2S and illustrate the design strategies and application examples of these probes. Moreover, we also emphasize the challenges and development directions of gasotransmitter-responsive fluorescent probes, hoping to provide a general implication for future research.

Luminescent Sm(III) complex bearing dynamic imine bonds as a multi-responsive fluorescent sensor for F- and PO43- anions together with Zn2+ cation in water samples

We have designed and synthesized a new luminescent mononuclear samarium (III) complex Sm-2_h based on the [1 + 1] Schiff-base macrocycle H₂L2_h, derived from the cyclocondensation reaction between dialdehyde and diamine precursors, and its exact architecture is determined to be [Sm(HL2_h) (NO₃)₂]. The sensing ability of complex Sm-2_h is carefully evaluated for various common inorganic ions in solution. It is shown that complex Sm-2_h is a multi-responsive fluorimetric sensor with high selectivity for F^- and PO₄^3- anions together with Zn²⁺ cation. The sensing process is rapid within 60 s for F^- and PO₄^3- ions and 300 s for Zn²⁺ ion. Further detailed responsive investigations suggest that its sensing behavior has excellent linear relationship between the fluorescence intensity (or absorption value) and ion concentration. The limit of detection (LOD) for sensing F^-, PO₄^3- and Zn²⁺ ions are as low as 2.61 μM (2.94 μM), 1.92 μM (1.64 μM) and 5.67 μM (3.53 μM), respectively, verified by fluorimetric (or colorimetric) titration experiments. ESI mass spectra prove that these efficient detections originate from the structure collapse of sensor Sm-2_h because of the ion-induced imine bond breakage. Moreover, sensor Sm-2_h shows excellent sensing performances for F^-, PO₄^3- and Zn²⁺ ions in real water samples, and we also have developed a convenient method to detect these three ions by use of the sensor impregnated test paper strips, providing rapid and distinguishable fluorimetric color changes. Therefore, the macrocyclic Sm(III) complex Sm-2_h could be regarded as a valuable candidate for monitoring F^-, PO₄^3- and Zn²⁺ ions in practical applications.

Highly sensitive turn-on detection of mercury(II) in aqueous solutions and live cells with a chemosensor based on tyrosine

Herein, we reported a novel fluorescent chemosensor (DY) based on dansyl group and tyrosine by solid phase peptide synthesis (SPPS) for the detection of mercury(II) ions with excellent selectivity among 17 different metal ions. As designed, DY exhibited a sensitive fluorescence "turn-on" response to Hg²⁺ with low detection limits of 22.65 nM. A stoichiometric ratio (2: 1) of chemosensor DY and Hg²⁺ ions was determined by a Job's plot, fluorescent titration and the ESI-MS spectra. Especially, the reversible of DY-Hg with EDTA establishes the reuse of DY, and the circulation effect was very good. Furthermore, the wide pH range of 6-10 makes it capable of application in biological systems. Moreover, DY has been successfully applied to the detection of Hg²⁺ ions and EDTA in living HeLa and HK2 cells based on low cytotoxicity and good membrane permeability.

Synthesis of Insulated Heteroaromatic Platinum-Acetylide Complexes with Color-Tunable Phosphorescence in Solution and Solid States

Phosphorescence colors of cyclodextrin-based insulated Pt-acetylide complexes were tuned by the molecular engineering of the chromophores. A series of Pt complexes bearing various acetylide ligands, including heteroaromatics, were prepared via self-inclusion of the linked macrocycles with the complexes. The decline in the inclusion efficiency derived from the heteroaromatics was overcome by the late-stage insulation via intramolecular slippage after the construction of the Pt-acetylide complexes. The cyclic protection of the thus-formed complexes prevented phosphorescence quenching via molecular interactions, even in the solid state. Accordingly, the tuned emission colors in a dilute system were replicated in the solid state.

A novel fluorescent chemosensor for detection of mercury(II) ions based on dansyl-peptide and its application in real water samples and living LNcap cells

Mercury is one of the most hazardous pollutants, and mercury pollution is a serious hazard to our environment. Herein, we designed and synthesized a new peptide-based fluorescent chemosensor (L) based on a Fmoc-Lys (Fmoc)-OH backbone conjugated with two Serines and dansyl groups using solid phase peptide synthesis (SPPS) technology. L exhibited highly selective and excellent sensitive detection of Hg²⁺ ions in 100% aqueous solutions through fluorescence quenching. The chemosensor L forms a 2:1 stoichiometry with high binding constants (4.89×10⁶M^-1) and the detection limit for Hg²⁺ ions of the proposed assay was 7.59nM. In addition, the recovery test results of Hg²⁺ concentration in actual water samples showed that the quantitative detection of Hg²⁺ ions can be realized in two water samples. Moreover, L showed low cytotoxicity and excellent membrane permeability in HK2 cells, which has been successfully applied for monitoring Hg²⁺ ions in living LNCaP cells.

Pyrrole-quinazoline derivative as an easily accessible turn-off optical chemosensor for Cu2+ and resultant Cu2+ complex as a turn-on sensor for pyrophosphate in almost neat aqueous solution

A simple chemosensor, 6-(1H-pyrrol-2-yl)-5,6-dihydro-benzo[4,5]imidazo[1,2-c]quinazoline (1), was synthesized via simple nucleophilic addition reaction coupled with Schiff base condensation. The probe 1 is aggregation-induced emission-active and could be used as an on-off fluorescence sensor toward Cu²⁺ in H₂O/CH₃CN (99.5%, v/v) solution. Furthermore, the resultant Cu²⁺ complex selectively responded to pyrophosphate (PPi) among various anions based on fluorescent on-off signal. In addition, the probe could be used for detecting Cu²⁺ and PPi in HeLa cells.

Zinc(ii), copper(ii) and cadmium(ii) complexes as fluorescent chemosensors for cations

The fluorescence chemosensing behavior of Zn(ii), Cu(ii), and Cd(ii) based complexes toward cations has been described. Cation detection via conventional mechanisms, metal-metal exchange and chemodosimetric approaches along with the importance of metal ions and the scope, significance, and challenges with regard to the detection of cations by metal complex based probes will be discussed in detail. The fundamentals of photophysical behavior and mechanisms involved in the fluorescence detection of analytes will also be described. This article provides a detailed overview of Zn(ii), Cu(ii), and Cd(ii) based complexes as fluorescent probes for cations, together with essential discussions pertaining to detection mechanisms.

Making the Right Link to Theranostics: The Photophysical and Biological Properties of Dinuclear RuII-ReI dppz Complexes Depend on Their Tether

The synthesis of new dinuclear complexes containing linked Ru^II(dppz) and Re^I(dppz) moieties is reported. The photophysical and biological properties of the new complex, which incorporates a N,N'-bis(4-pyridylmethyl)-1,6-hexanediamine tether ligand, are compared to a previously reported Ru^II/Re^I complex linked by a simple dipyridyl alkane ligand. Although both complexes bind to DNA with similar affinities, steady-state and time-resolved photophysical studies reveal that the nature of the linker affects the excited state dynamics of the complexes and their DNA photocleavage properties. Quantum-based DFT calculations on these systems offer insights into these effects. While both complexes are live cells permeant, their intracellular localizations are significantly affected by the nature of the linker. Notably, one of the complexes displayed concentration-dependent localization and possesses photophysical properties that are compatible with SIM and STED nanoscopy. This allowed the dynamics of its intracellular localization to be tracked at super resolutions.

A robust photoluminescence screening assay identifies uracil-DNA glycosylase inhibitors against prostate cancer

Many cancers have developed resistance to 5-FU, due to removal by the enzyme uracil-DNA glycosylase (UDG), a type of base excision repair enzyme (BER) that can excise uracil and 5-fluorouracil (5-FU) from DNA. However, the development of UDG inhibitor screening methods, especially for the rapid and efficient screening of natural product/natural product-like compounds, is still limited so far. We developed herein a robust time-resolved photoluminescence method for screening UDG inhibitors, which could significantly improve sensitivity over the screening method based on the conventional steady-state spectroscopy, reducing the substantial fluorescence background interference. As a proof-of-concept, two potential UDG inhibitors were identified from a database of natural products and approved drugs. Co-treatment of these two compounds with 5-FU showed synergistic cytotoxicity, providing the basis for treating drug-resistant cancers. Overall, this method provides an avenue for the rapid screening of small molecule regulators of other BER enzyme activities that can avoid false negatives arising from the background fluorescence.

The discovery of UDG inhibitors against prostate cancer by using a robust photoluminescence screening assay that can avoid false negatives arising from the background fluorescence.

Eight Cd(ii) coordination polymers with persistent room-temperature phosphorescence: intriguing dual emission and time-resolved afterglow modulation

A new series of p-RTP CPs 1–8 were designed and successfully synthesized; 5–8, in particular, exhibited intriguing time-resolved afterglow modulation.

Vapor switching of the luminescence mechanism in a Re(v) complex

A Re(v) mononuclear complex switches the characters of emissive states by methanol vapor via a single-crystal-to-single-crystal ligand exchange reaction.

An efficient water-soluble fluorescent chemosensor based on furan Schiff base functionalized PEG for the sensitive detection of Al3+ in pure aqueous solution

An efficient reversible fluorescent chemosensor, PEGFB, based on polyethylene glycol bearing a furan Schiff base unit has been successfully developed to sensitively detect Al³⁺ in pure aqueous solution.

Assembly of Three Lanthanide Coordination Polymers from 2-(4-Carboxybenzyloxy) Benzoic Acid Ligand: Synthesis, Structure, and Fluorescent Properties

Three new coordination polymers, {[Ln(cbb)(Hcbb)(DMF)·H2O]n, Ln=Sm (1), Eu (2), Tb(3), H2cbb=2-(4-carboxybenzyloxy) benzoic acid, DMF=N,N-dimethylformamide}, have been synthesised by a solvothermal reaction and structurally characterised by infrared spectroscopy, elemental analysis, thermogravimetry analysis, and X-ray single-crystal diffraction. The results of single-crystal X-ray diffraction indicate that the coordination polymers 1–3 are isostructural, belong to a triclinic system, space group P-1, and show 1D chain structures through the H2cbb ligands connecting adjacent lanthanide ions. In addition, the fluorescence properties of polymers 1–3 were also investigated.

Dinuclear metal complexes: multifunctional properties and applications

Dinuclear metal complexes have enabled breakthroughs in OLEDs, photocatalytic water splitting and CO₂reduction, DSPEC, chemosensors, biosensors, PDT and smart materials.

Reactivity of ZrO(MFP) and ZrO(RP) Nanoparticles with LnCl3 for Solvatochromic Luminescence Modification and pH-Dependent Optical Sensing

The luminescence of the inorganic-organic hybrid nanoparticles ZrO(MFP) (MFP=methylfluorescein phosphate) and ZrO(RP) (RP=resorufin phosphate) was modified by addition of different rare earth halides LnCl3 . The resulting composite materials form dispersible nanoparticles that exhibit modified nanoparticle fluorescence depending on the rare earth ion. The resulting chromaticity of the luminescence is further variable by the employment of different solvents for ZrO(MFP)-based composite systems. The strong solvatochromic effect of the MFP chromophore leads to different luminescence chromaticities of the composite materials between green, yellow, and blue in THF, toluene, and dichloromethane, respectively. The luminescence of ZrO(RP)-based composite particles can be modified between the red and blue spectral regions in dependence on the applied reaction temperature. Beside a luminescence shift that is derived from nanoparticle modification by LnCl3 , a strong turn-on effect of ZrO(RP) particles results after contact with different Brønsted acids and bases in combination with a respective chromaticity shift. Both effects enable the potential employment of such particles as highly sensitive optical pH sensors.

Efficient and very selective dual mode chemosensor for Cd(II) ions in live cells

A sensitive dual mode chemosensor NS-1 comprising Nitrobenzoxadiazole and salicylhydrazide conjugate has been synthesized via single step reaction. The probe NS-1 is characterized by analytical techniques such as multi nuclear NMR techniques and Mass spectrometry. The probe is showing a strong change in color from yellow to red on treatment of Cd(II) ions, interestingly its shows bright "Switch-ON" fluorescence state upon binding of Cd²⁺ ions in buffer solution whereas other cations did not showed any color change as well as fluorescent change. Interestingly the probe NS-1 did not results in the any color and fluorescence change with the adding together of Zn(II) ions, hence the probe is able to differentiate between Cd(II) ions from Zn(II). Further the color change and turn-on fluorescence can be rationalized by the interruption of internal charge transfer upon binding of Cd(II) ions with NS-1. The Internal charge transfer disturbance led to fluorescence change of the receptor NS-1 upon addition of Cd²⁺ has been further supported by TD-DFT calculations. The limit of detection was found to be 6.31 nano molar. The association constant was found to be 7.97*10⁴ M^-1 using Benesi-Hildebrand plot method. MTT assay suggesting that the probe NS-1 is least toxic to cells and it will be widely applicable to image Cd(II) ions in living cells via fluorescence imaging.

Photostable Voltage-Sensitive Dyes Based on Simple, Solvatofluorochromic, Asymmetric Thiazolothiazoles

A family of asymmetric thiazolo[5,4-d]thiazole (TTz) fluorescent dye sensors has been developed, and their photophysical sensing properties are reported. The π-conjugated, TTz-bridged compounds are synthesized via a single-step, double condensation/oxidation of dithiooxamide and two different aromatic aldehydes: one with strong electron-donating characteristics and one with strong electron-accepting characteristics. The four reported dyes include electron-donating moieties (N,N-dibutylaniline and N,N-diphenylaniline) matched with three different electron-accepting moieties (pyridine, benzoic acid, and carboxaldehyde). The asymmetric TTz derivatives exhibit strong solvatofluorochromism with Stokes shifts between 0.269 and 0.750 eV (2270 and 6050 cm^-1) and transition dipole moments (Δμ = 13-18 D) that are among the highest reported for push-pull dyes. Fluorescence quantum yields are as high as 0.93 in nonpolar solvents, and the fluorescence lifetimes (τ_F) vary from 1.50 to 3.01 ns depending on the solvent polarity. In addition, thermofluorochromic studies and spectrophotometric acid titrations were performed and indicate the possibility of using these dyes as temperature and/or acid sensors. In vitro cell studies indicate good cell membrane localization, negligible cytotoxicity, promising voltage sensitivities, and photostabilities that are 4 times higher than comparable dyes. Their ease of synthesis and purification, remarkable photophysical properties, and chemically sensitive TTz π-bridge make these asymmetric dye derivatives attractive for environmental and biological sensing or similar molecular optoelectronic applications.

Fabrication of a Hydrazone-Based Al(III)-Selective "Turn-On" Fluorescent Chemosensor and Ensuing Potential Recognition of Picric Acid

A hydrazone-based N'1,N'3-bis((E)-4-(diethylamino)-2 -hydroxybenzylidene)isophthalohydrazide (NDHIPH), has been synthesized, characterized, and assessed for its highly selective and sensitive (limit of detection, 2.53 nM) response toward Al(III) via fluorescence enhancement in 95% aqueous medium. All experimental results of analytical studies are in good consonance with the theoretical studies performed. Further, this NDHIPH-Al(III) ensemble is used for selective and sensitive (12.15 nM) detection of explosive picric acid (PA) via fluorescence quenching. This reversible behavior of NDHIPH toward Al(III) and PA is used for the creation of a molecular logic gate.

Design and Applications of Small Molecular Probes for Calcium Detection

The physiological significance of calcium ions such as the role in cellular signalling, cell growth, etc. have driven the development of methods to detect and monitor the level of Ca²⁺ ions, both in vivo and in vitro. Although various approaches for the detection of calcium ions have been reported, methods based on small molecular fluorescent probes have unique advantages including small probe size, easy monitoring of detection processes and applicability in biological systems. In this review article, we will discuss the progress in the development of Ca²⁺ -binding fluorescent probes by taking into account the types of chelating groups that have been employed for Ca²⁺ binding.

Metal-Dependent DNAzymes for the Quantitative Detection of Metal Ions in Living Cells: Recent Progress, Current Challenges, and Latest Results on FRET Ratiometric Sensors

Many different metal ions are involved in various biological functions including metallomics and trafficking, and yet there are currently effective sensors for only a few metal ions, despite the first report of metal sensors for calcium more than 40 years ago. To expand upon the number of metal ions that can be probed in biological systems, we and other laboratories employ the in vitro selection method to obtain metal-specific DNAzymes with high specificity for a metal ion and then convert these DNAzymes into fluorescent sensors for these metal ions using a catalytic beacon approach. In this Forum Article, we summarize recent progress made in developing these DNAzyme sensors to probe metal ions in living cells and in vivo, including several challenges that we were able to overcome for this application, such as DNAzyme delivery, spatiotemporal control, and signal amplification. Furthermore, we have identified a key remaining challenge for the quantitative detection of metal ions in living cells and present a new design and the results of a Förster resonance energy transfer (FRET)-based DNAzyme sensor for the ratiometric quantification of Zn2+ in HeLa cells. By converting existing DNAzyme sensors into a ratiometric readout without compromising the fundamental catalytic function of the DNAzymes, this FRET-based ratiometric DNAzyme design can readily be applied to other DNAzyme sensors as a major advance in the field to develop much more quantitative metal-ion probes for biological systems.

Simple fluorene oxadiazole-based Ir(iii) complexes with AIPE properties: synthesis, explosive detection and electroluminescence studies

Two novel phosphorescent Ir(iii) complexes, Ir(fom)₂(pic) and Ir(fof)₂(pic), containing fluorene oxadiazole groups have been synthesized and characterized. The photophysical properties of the complexes have been investigated. Interestingly, both complexes exhibited aggregation-induced phosphorescent emission. The X-ray diffraction study showed that the AIPE properties resulted from weak π-π and C-HN hydrogen-bonding interactions in the aggregated state restricting the rotation of the phenyl groups in the cyclometalating ligands. Owing to the sensitive and selective luminescence quenching of the complexes using picric acid (PA), the complexes were used for PA detection in aqueous media. Additionally, electroluminescence devices have been fabricated using the complexes at 5%-30% doping concentrations. The devices based on Ir(fof)₂(pic) obtained the highest luminance 11 877 cd m^-2 and current efficiency 23.2 cd A^-1, which implied that the incorporation of fluorine could improve the electron affinity and ameliorate the capability of electron injection or transporting.

BODIPY-functionalized 1,10-phenanthroline as a long wavelength sensitizer for near-infrared emission of the ytterbium(iii) ion

Two BODIPY (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) moieties were chemically appended to the 4,7-positions of 1,10-phenanhtroline resulting in two new ligands (BODIPY-Phen and 4I-BODIPY-Phen) with strong absorption at 507 nm and 540 nm, respectively. BODIPY-Phen emits fluorescence strongly centered at 507 nm, whereas the fluorescence of 4I-BODIPY-Phen was completely quenched due to the introduction of four I atoms at its 2,6 positions. The two ligands reacted readily with tris(1,1,1,5,5,5-hexafluoro-2,4-pentanedionate) ytterbium(iii) dihydrate through substitution reactions forming eight-coordinate complexes that emit strongly at 976 nm upon excitation at their absorption maximal positions. Both complexes exhibited a lifetime of ∼11 μs in dichloromethane at room temperature.